This invention pertains to a drift tube linear particle accelerator, and more particularly, to such an accelerator which is specially augmented with apparatus, provided in accordance with the present invention, that uniquely promotes easy normalization and maximization of the operational performance of a drift tube employed in the accelerator.
Drift tube linear particle accelerators, also known as linacs, are well known to those skilled in the art. Just speaking by way of general and introductory terms, such an accelerator typically includes an elongate, cylindrical housing, distributed centered on and along the central operational axis of which are plural, annular drift tubes which are typically supported in position by externally adjustable mounting structure located on the outside of the housing, which mounting structure usually permits several degrees of motion for "axial" positional adjustment of the tubes--i.e., multidirectional adjustment. The respective geometries of the tubes, and their intended relative positions along the operational axis of an accelerator, are known and readily determinable in accordance with well-known operational theory relating to the necessary and desired particle-accelerating electromagnetic field configuration which is intended to exist along the axis of the accelerator.
In current drift tube linacs, final positioning of a drift tube along the operational axis typically is performed through adjustment mechanism which includes pivot points and infinitely adjustable screws. This mechanism, however, complex and expensive, has proven to offer poor long-term stability, and, in addition, to be troublesome under certain maintenance circumstances, such as, for example, where disassembly becomes necessary at some point in time for servicing, such as for mending a radio-frequency seal or a vacuum seal, or for some other necessary procedure. Adjustment screws are notorious for shifting positions, and a consequence of this is that disassembly and reassembly normally requires a complete, subsequent, entire readjustment of the set-screw, etc., positioning mechanism in order to return the associated drift tube to its proper operational position.
Normally cooperating with each Nth drift tube in a drift tube linac, and often for each and every drift tube, is what is known as a post-coupler which includes a paddle-like blade carried on the end of an elongate wand which extends through the wall of a linac housing radially toward the circumferential side of an associated drift tube. Typically, as one progresses axially along a linac, successive post-couplers extend in alternately from diametrally opposite sides of the housing. Through rotational and translational adjustment of the position of the "paddle" relative to its associated drift tube, important field-configuration adjustments can be made. With respect to such post-coupler structure, it is conventional to provide for each such structure, on the outside of the linac housing, full-complement, always-in-place, dedicated adjustment mechanism, and, this is an expensive consideration in the overall structure of a linac.
With regard to the operations of the drift tubes, standing high on the list of matters which must be met carefully for successful performance are (1), precision in the positional relationship of each drift tube along and relative (circumferentially) to an accelerator's operational axis, and (2), field configuration manipulation through positional adjustment (translational and rotational) of any adjacent and associated post-coupler. Naturally, these considerations are well known and have been addressed in prior art drift tube accelerator structures, but the best of the known prior art solutions leave important things to be desired, which "things" are amply, simply and quite elegantly addressed by the apparatus of the present invention.
In general terms, the apparatus of the present invention is one for both normalizing and maximizing the performance of a drift tube along the operational axis of the elongate housing in a drift tube linear particle accelerator. The phrase "normalizing and maximizing" is intended to convey the important notion that the apparatus promotes a situation where each associated drift tube performs substantially exactly in accordance with what is expected of it, and in a manner which maximizes its contribution to the particle-accelerating field in an accelerator.
As will become quite fully apparent from the drawings and description to be encountered in what follows, a preferred embodiment of the apparatus of the invention contemplates, for each drift tube in an accelerator, what is referred to as a datum unit which is fixed in position on the outside of an accelerator housing, with this unit including three, known-position, orthogonally-related datum surfaces that provide the datum foundations for defining the adjusted end position of the associated drift tube. Cooperating with this datum unit is a seating structure that is adapted for fixed-position joinder to a drift tube through the usual stem which supports the tube inside an accelerator. The seating structure includes three, complementing, orthogonally related datum surfaces designed for confrontational positioning, through fixed-dimension shim structure, with respect to the three datum surfaces in the datum unit.
Tightenable/relaxable anchoring mechanism drives the seating structure against the shim structure, along three orthogonal axes, and through such shim structure against the datum surfaces in the datum unit, thus to define forever, for all practical purposes, and so long as the shim structure remains unchanged, an accurate position for the associated drift tube. Obviously, because of the dimensional stability which characterizes the shim structure, it is comfortably possible to disassemble a drift tube from the housing, for reasons such as those mentioned earlier, with confidence, and strong assurance, that return to an anchored-in-position condition, utilizing exactly the same shim structure, will result in the drift tube being easily, properly repositioned. Quite apart of the disassembly/reassembly issue, the proposed shim-structure arrangement offers long-term stability not found in prior art drift tube linacs.
To deal with the issue raised above regarding adjustment for a post-coupler structure, the preferred embodiment of the present invention further includes special post-coupler adjustment mechanism which is removably, operatively attachable as desired to the externally accessible components of each post-coupler structure, with appropriate mechanism components provided that allow for ready angular and translational adjustment of each such post-coupler structure. Obviously this novel, nondedicated, attachable/removable approach significantly reduces the expense which would otherwise attend a conventional structure wherein each post-coupler structure has its own dedicated adjustment mechanism.
These and other objects, features and advantages which are offered by the invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawings.